1. Field
The invention is in the field of automotive transmissions and particularly of so-called "compound" transmissions which utilize a main transmission and an auxiliary transmission in combination.
2. State of the Art
Compound transmissions for increasing the range of available speeds are old in the art, but, as heretofore constructed, have been for use in heavy duty trucks. These have motors of low RPM requiring almost stopping of the vehicle to change gears if usual "jamming" is not successfully accomplished. To adapt this type of transmission for use in what are generally recognized as light duty trucks, namely, pick-up trucks or other trucks of up to two ton class, planetary gearing has been used to conserve space so the compound transmission will fit into the usual envelope space provided by the truck. This, however, results in undesirable sacrifice of structural strength for the transmission.
Some attempts have been made to obtain a greater range of available speeds without compounding transmissions, as in U.S. Pat. No. 3,046,807 issued to E. J. Barth and Carl J. Gustaffson on Jul. 31, 1962 for a "Double Countershaft Multispeed Transmission". However, the transmission of that patent is for use in heavy duty vehicles.
In U.S. Pat. No. 4,152,949 of May 8, 1979 issued to John R. Vandervoot and Alan R. Davis on May 8, 1979 for an "Extended Range Transmission", the transmission is of so-called "simple" type having a one-piece main shaft. It is not a compound transmission combining main and auxiliary transmissions, and, again, it is for use in heavy duty vehicles.